Giant Silkmoths are spectacular insects as large, colorful caterpillars and even larger and more colorful moths. Adults are commonly encountered during late spring and summer resting on the sides of buildings beneath outdoor lights. Larva are most noticeable in the fall and some species can exceed 6″ in length. Interestingly, the moth has no mouth or digestive system. Energy stored from the caterpillar stage is used to fuel the adult moth. If all goes well she may deposit several hundred eggs a few at a time on native trees and shrubs before she dies. Predators of adults abound in nature. By day birds prey on resting moths and the cover of night offers little protection from nocturnal predators like bats. With very few exceptions, caterpillars are not adapted to feed on anything except our native plants. What we hope to do here is encourage you to plant native trees and shrubs in your home landscape with the intention of attracting and maintaining all life stages of these insects.
If your interest is in seeing these beautiful insects, enjoying them as they progress through their life cycle and emerging next spring as adult moths then you must provide the proper food source for their caterpillars. We have compiled pictures of the most common silk moths along with appropriate host plants to feed them. Riverside Native Trees and Nursery grows many of the tree and shrub species listed here so that you can provide the appropriate host plants in your landscape. Caterpillars can be easily raised with minimal effort from you and the information contained here is designed to help you be successful. Please note though, there are lots of hungry birds, parasitic flies and wasps and other creatures that would love to eat your caterpillars so they’ll need to be protected. The instructions provided here are gleaned from the experiences of many people who raise moths and their caterpillars during the summer.
Caterpillars are festooned with bumps, spikes, tubercles, hairs and other ornaments and some can look quite ferocious (see the Hickory Horned Devil below) but they are harmless. The only exception is the larva of the IO moth. It is mildly toxic and will cause itchy bumps if you touch their spines; sort of like stinging nettles. Fortunately, it is the least common species we’ve encountered. All the rest are completely harmless and have made great pets!
How you can help!
One of the goals at Riverside Native Trees and Nursery is to provide you with native trees and shrubs that many insect species need to complete their life cycle. All of these moths are in decline across North America primarily due to habitat destruction. Naturally occurring host plants for caterpillars are dwindling as trees and shrubs and natural places are removed in the name of “progress”. In rural areas, farming practices that encourage the removal of brush along fence lines and roadsides reduce caterpillar food resources. What we can do in the short term that will have an immediate, positive effect is to plant trees and shrubs in our home landscapes and parks that are known host plants for the caterpillars. A popular movie years ago included the line “if you build it they will come”. In my experience “if you grow it they will come” is also true and we are encouraging you to do just that! Younger trees seem to be more attractive to egg laying females so planting small is a benefit!
Rearing Your Own Caterpillars and Moths
If your intention is to raise caterpillars and observe their life cycle you will need to provide them with protection from predators and parasites. To accomplish this use a “caterpillar sock”. A caterpillar sock is a netted bag with drawstrings that can be placed over the leafy end of a host plant branch and tied shut. Care must be taken to examine the leaves and branches to be enclosed for insect predators before you place caterpillars into the sock. In fact, even before you put the sock on the branch it is helpful to vigorously shake the branch for 15-30 seconds to dislodge any spiders, stinkbugs, or other insects that would want to make a meal of your caterpillars. Once the sock is slipped over the branch and has all the leaves inside you can place the eggs or larva inside as outlined below.
How to obtain eggs.
If you would like eggs I can send these to you. What you’ll need to do is look at the trees and shrubs in your landscape to determine if you have the species they require as host plants. If so, send me a letter with a SASE (2 stamps please) and I will do my best to send you eggs when they are available. In your letter please include the species of host plant you have and your name, email and phone number so we can contact you when they are en route. The window for getting eggs is very limited so send your envelope now and when I have eggs I will send them to you. Use the link below to order your caterpillar sock(s) now so that you’ll be ready to go when your eggs arrive. Note: I can only send eggs to Ohio residents. If you’re from another state you’ll need to supply proper permits. State permitting is not difficult and it’s free but it may take up to three months to complete.
If you happen to find a live female moth she is probably fertile and you could collect eggs from her by putting her in a brown lunch bag for a day or so. After that time release her after dark to finish distributing her eggs. You don’t need very many eggs…6-10 would be plenty for one sock especially when they are large. See the information in the ‘mating’ paragraphs below for more information on using brown paper bags to get eggs.
Giant Silk moths (Saturniidae) have a complete life cycle or go through complete metamorphosis. This means they have four distinct life stages, egg, larva, pupa and adult. Each stage is distinctly different from the others. Many insects have complete metamorphosis including flies, bees and beetles. Other insects have an incomplete life cycle or incomplete metamorphosis. This type of life cycle has only three life stages including an egg, a nymph, which looks like a miniature, wingless version of the adult and an adult stage. Grasshoppers, mantids and walkingsticks have incomplete metamorphosis.
Once a female has been successfully fertilized she will begin to lay viable eggs. Eggs are fastened to leaves and stems of appropriate host plants, generally near the tips of the branches. In general, only a few eggs are deposited on a host plant to avoid predation or parasites. Since caterpillars have little in the way of defense they instead hide in plain sight by blending in to escape detection. Too many caterpillars on a single tree would draw the attention of predators and parasites. Even though the eggs are tiny there are insects that would use them as food if they could so they need to be protected. Tiny parasitic wasps search out eggs to serve as food resource for their own young. When they find an egg they sting it and in so doing deposit their own egg inside the moth egg. The wasp egg hatches and devours the contents of the moth egg later emerging as an adult wasp. Regular netting or insect screening is not fine enough to exclude egg parasites. Commercially made caterpillar socks like those offered for sale here are made of a very fine mesh screening and work well to protect eggs. The picture at the above right shows an egg parasite. It appears as a tiny, black line across the eggs but you can see the wasps’ antenna.
Eggs take approximately two weeks to hatch depending on temperature. If you used the brown paper bag method (see ‘mating’ section below) you can staple the cut pieces of paper bag containing the eggs to the underside of an appropriate host plant or loop them around the end of branch nearest the new growth. Be careful not to crush the eggs. If you prefer you could hatch the eggs indoors and thus get them through this first life stage successfully. To do that, gather the eggs while still on their paper and place them in a ziploc type, sandwich sized baggies. Seal the bag so that it remains somewhat inflated with air. Leave the baggie in an area where it will not get damaged AND where you can see it several times a day to check for hatching.
When you see the larva begin to hatch gently open the bag and place a few leaves into the baggie from the host plant you’ll be using. They’ll crawl on and begin to feed. It may take a day or so for all eggs in the batch to hatch so the young caterpillars will need this food provided by you. Larva are much more easily handled by picking up the leaf. Place the leaf with the hatchling caterpillars right into the prepared caterpillar sock. Don’t forget to examine the leaves for predators! Since the larvae are so small and I’m not confident they could crawl very far to find food I use an unconventional method to get them onto good leaves. Tear or rip a small hole in the leaf that the larvae are being transferred to (which would be inside the sock) and thread the leaf they are currently on through that tear. Both the original leaf the larva are on and the new leaf are wedged together in the torn leaf. The larva will crawl onto the new leaves as they feed and transfer will be complete. You could also staple the hatchling leaf to a new leaf. If a few caterpillars are left in the plastic baggie you can gently place it on a leaf inside the sock and they’ll crawl to the leaves looking for food. The first time you change the leaves or clean the caterpillar sock you can remove the plastic baggie.
For a week or more it will be hard to even find the larva in the sock. That is to be expected because they are only a couple of millimeters long when they hatch. The only evidence you will see are their tiny droppings (frass) which look like black grains of salt. But they do grow rapidly and in about 10 days to 2 weeks you’ll begin to see the substantially larger caterpillars feeding on the underside and edges of the leaves. Just a few days later you will note that the leaves in the sock are dwindling and that a large amount of frass and leaf parts are accumulating at the bottom of the sock. Gently remove the sock and empty the waste. With the sock off you can now see the larvae very clearly and note their striking color and how perfectly they blend with the leaves. If there are still a lot of good leaves left you can put the sock back on, secure the drawstrings tightly and let them go for a few more days before you consider changing to fresh leaves. As the caterpillars get larger they will consume leaves at a faster rate so check the socks regularly. You’ll know it’s time to change to new leaves if the caterpillars are eating the leaf stems (petioles). They aren’t injured by waiting this long but they seem to prefer the leaves over the stems so change them a little sooner next time. Attach the sock over the new leaves (inspect for predators first) and secure the drawstring(s).
When moving larva to new leaves we find that is easiest to transfer the caterpillars by removing the leaf they are feeding on in the old sock and placing that leaf right into the new sock after it has been put over the new leaves. Caterpillars that are on the leaf petioles can be removed by snapping the petiole off at the branch. At this point the caterpillars are large enough that they can easily crawl to find new leaves so we just place them in the sock and tie the drawstrings.
A few caterpillars may be walking along the branches and they’ll need to be gently removed and placed in the sock. They can actually move pretty quickly and some will get away if you’re not quick about refreshing their leaves. You CANNOT just pull the caterpillar off the branch. Doing so could actually tear their legs off because there are little hooks on their feet that fasten securely to the branch. The solution is to use your thumb and forefinger and gently apply pressure to the back legs of the caterpillar in a rubbing/gently pinching motion. When pressure is applied to their legs the caterpillar responds by releasing its grip on the branch for that leg. You may need to do this for each leg but once one of the legs lets go the others are fairly easily removed. Caterpillar socks are great for keeping most predators out. Some insects though, like stinkbugs, have a long proboscis and can actually pierce the skin of a caterpillar that is near the edge of the sock and kill it. If you see stinkbugs on your socks it’s best to kill them.
Sometimes a hole will develop in the netting from a chewing caterpillar. Use duct tape on both the inside and the outside of the netting to seal it. At the end of the season we dump all the material out of the sock and put them in the washing machine. (My wife is a saint) I pull the drawstrings tight and place them into the sock so they are not hanging out to get tangled. We have a front loading washer which just tumbles them around without getting them all balled up. Washing them by hand is an option too. All of this helps to keep disease down so it’s a good idea to do this at the end of the season and determine if your socks will make it through another season. We’ve had some socks last for over 5 years so they do weather well.
Caterpillars grow through five distinct stages, or instars, as they mature. Depending upon the species the younger instars may or may not look like the older ones. Assuming the caterpillar is healthy at some point it will stop eating and prepare for the pupa stage. Some of the changes that take place in preparation for this include purging the gut contents and often a period of wandering. A mature caterpillar ready to pupate (change from a larva into an adult insect) regurgitates any undigested food in its stomach and this will appear as a dark green stain on the inside of the caterpillar bag. When I see this I know that at least one caterpillar is going to pupate soon so I look to see who is wandering inside the sock. Wandering is a behavior that many caterpillars go through to look for a suitable place to spin their cocoon. They may even be trying to bury themselves in the litter at the bottom of the sock. If you’re raising Cecropia, Promethea, Luna or Polyphemus you can just leave them in the sock and they’ll spin their cocoons there. If you’ve got Imperial caterpillars or Hickory Horned Devil’s they’ll need a little more work from you.
Imperial and Royal Walnut Moth larva pupate underground. In the fall the larva wander down the tree and burrow through leaf litter into the soil. To simulate this behavior use a 5 gallon bucket and a commercial potting mix in which to burrow. Pour a layer of potting mix 4-6″ deep in the bucket and lightly wet it. Add enough water to the mix so that it is moist but not soaking wet. The consistency you’re striving for is this: if you tightly squeeze a handful of mix just a few drops of water should appear. If you squeeze it and water does not come out then add a little more water to the mix and re-squeeze. Perform the squeeze test for all of the mix in the bucket before putting the larva in. Also, break up the clumps of mix in the bucket. You want an evenly moist, fine consistency mix for your caterpillars. You do not want water to accumulate in the bottom of the bucket which could drown the pupae but enough moisture in the mix to raise humidity levels around the pupae.
Remove larva ready to pupate from the sock and place them on the moistened mix in the bucket. Cover the bucket to prevent them from escaping and you’ll find that within a few hours they’ll be underground. Once they are underground they will shed their final larval skin exposing the dark brown pupal skin. If you dig them up to look at them you’ll find that they are quite active and the abdomen moves in response to being handled. They are vulnerable to being crushed so be gentle with them. Bury them back under a few inches of the loose potting mix and place the bucket in a warmer corner of an unheated garage and somewhere it will not be rained upon. In the nursery we have 4″ deep square trays with a mesh floor for underground pupation. We put two of them together and clamp them shut with binder clips. We leave this outside during the late summer and fall where they get rainfall and experience temperature fluctuations. Since the floor of the tray is mesh rain water does not accumulate in the mix. Do not try this if you’re using a bucket to overwinter your pupae as the water will accumulate to a point the larva drown. When cold weather arrives we bring the tray(s) into the garage.
In central Ohio, Promethea, Luna and Polyphemus moths may have two broods during the summer. Cocoons produced during June may emerge as adults in a few weeks to produce the second generation of the year. All the other species have just one brood per year which produce cocoons in late summer or fall. The information in this paragraph only applies to cocoons collected during the fall and that you will overwinter. Silk moths that produce cocoons in the fall go through a period of diapause. Diapause is a resting period prior to developing into the next (in this case the adult) stage. During this time the pupae is relatively inactive. Chemical inhibitors inside the pupae keep it from developing so that it does not emerge as an adult at the wrong time. Cold temperatures slowly degrade the chemical inhibitors and once those chemicals are gone development of the adult moth can proceed. The important point here is that Fall pupae MUST have sufficient cold in order to break diapause. If they do not have enough cold they will not emerge as adult moths. In general, if you overwinter your cocoons or underground pupae in an unheated garage they will receive enough cold to begin adult development. Our pupae are stored in an empty 10 gallon aquarium in an unheated garage during the winter. This exposes them to sufficient cold to break diapause but not so much cold as to kill them. This can be simulated in a refrigerator but the trouble is that your moths may not emerge at the same time as the other, wild moths in your area. During the very cold winter of 2013 we left the cocoons in the aquarium on the back porch all winter. All of the Luna’s died but the Cecropia’s did fine. This year we protected them in the garage which should give us greater survival rates. When winter breaks and average low temperatures are above freezing (mid-March to early April) we bring the aquarium out of the garage and put it on the back screened in porch.
The glass walls of the aquarium are too smooth for the adults to pull themselves up easily so we place a few sticks into the tank to give them something to crawl up. Immediately after emerging from the cocoon an adult moth will crawl around looking for a vertical surface to climb to aid in wing expansion. Ideally, having the moths hang upside-down from the screened lid would allow gravity to help with expanding their wings. Fluid from the abdomen is forced into the wings to “inflate” them and in a few hours they will be flight-worthy. If wing expansion does not occur within an hour or two after emergence the wings will “dry” like this and this moth will not be able to fly and thus mate. It is imperative that the moths get to a vertical surface quickly or hang upside-down. Lining the inside of the aquarium with insect netting or screening would allow for an easy climb. It’s the beginning of the end for these moths. All that’s left is for them to mate and distribute their eggs and only about two weeks in which to complete it before they die.
Mating and collecting eggs
Once moths have emerged from their cocoons they take a day or so before they actively seek a mate. Females with their large abdomens full of eggs produce a scent from an organ at the tip of their abdomen that the males home in on. This is termed ‘calling’ and you can see this organ everted at the very tip of her abdomen when she is actively calling. Calling for most silk moth species occurs in the late afternoon and/or throughout the evening hours. Promethea moths are unusual in that they are active during the daylight hours. Males are thought to mimic the pipevine swallowtail which birds generally find to be distasteful; so he can fly with impunity. The large, feathery antennae of males sifts the air for molecules of this scent and when he detects them he flies in the direction that increases the concentration. When he finds her there is a lot of fluttering as he gets his bearings but eventually he couples with her and mating begins. They may be joined for as long as a day and when finished they’ll separate.
Adult moths are among the preferred foods of many species of birds so care must be taken to protect them during this vulnerable time. Mating takes place generally at night or in areas of vegetation where birds will not see them. Here at the house we have a screened in back porch and that is where the cocoons are brought in late winter/early spring to emerge. This also provides a great place for females to be protected and to call males. Since I do not want my female moths to mate with male moths from the same brood (their siblings) I collect wild males that are called in. In the early morning while it just getting light I will go out and look at the outside of the porch screen for males. Some days there are 3 big Cecropia males flapping against the screen trying to get in. I collect those and bring them into the porch and let them go. I check a few times a day to see if they’ve found each other and once before bedtime and again in the early morning.
If you do not have a screened in porch handy there are other methods you can use that will allow successful mating. Some people simply leave the females in an open garage overnight and the males find them there. You would want to check early in the morning to see if they are mating and prepare to capture her when she is finished. If mating has not occurred the first night the female may fly out the next evening to better her chances. Others have built a screen cage that protects the female but has large enough holes to allow the male to mate through the wire mesh. Hardware cloth (with 1/2″ X 1/2″ square holes) has large enough mesh to allow the moths to mate. Fashion the hardware cloth into a round tube or ring and place another piece over the top and bottom of the ring and secure the pieces together with wire or zip ties. Place the female inside the cage and hang the whole cage from a low branch on a tree. Don’t put the cage on the ground as air currents are necessary to carry her scent to the males. In the early morning check the cage to see if she is mating. If they are mating gently move the cage to a garage or shelter to keep them away from the hungry birds.
We’ve also had good luck with putting males and females together in a 20 gallon (long) aquarium with a screen top; hanging the female from the screen. It’s a bit small for large cecropia moths but promethea and lunas mate readily in this enclosure. When they are finished mating you can let the male go but place the female in brown paper lunch bag or grocery bag (not the plastic ones). She will begin to lay her eggs the first night she’s in there; sometimes the second night. You’ll hear her fluttering around in the bag and all this fluttering does damage her wings so as soon as you have the eggs you need let her go that evening after dark. How many eggs you need is up to you but 6-10 is a lot especially for one sock at the end of the season with big caterpillars inside. We’ve raised as many as 75 Luna’s in a single large 6′ sock but even then we were changing it every day to keep later instar larvae in fresh leaves. Sometimes you will find that unmated females begin to lay eggs and these will not hatch. If you are unsure whether or not they are fertile eggs collect and place them in a plastic baggie. If they’ve not hatched in two weeks or so or if you see the beginning to shrink or appear deflated they are duds and can be discarded.
The eggs you hold in your hand are the promise of the next generation of moths. Remember that part of the reason that we are doing this is because native moths need our help but another good reason to do this is because of your kids and grandkids. I encourage you to show these beautiful insects to your children and grandchildren and tell them what you’re doing and why your doing it. Give them a mini science lesson in the process. With the information you’ve read here you know more than enough to wow a little kid! Keep a garden notebook with important dates, any observations or sketches you’ve made or pictures taken. All of this helps to create interest in a child and will become a keepsake when they are old enough to see how smart you really were! How many times have we heard someone say “Well, I do this because this is the way my grandparents did it” or “this is what my grandparents did”. We’re investing time now in children that can pay big dividends in the future. In this age of way too many computer games we can all agree that it would do a kid good to be outside and take an interest in natural things. Let’s foster a child’s curiosity in nature by giving them something to take care of and something that their friends probably will not have; interesting insects to raise. It will take some planning on your part but the rewards far outweighs the costs and we’re here to help you! Who knows? You could be fostering the curiosity of the next generation of scientists or nurserymen and women in the process!